Laser Deposition of Metal Halide Perovskites

Vacuum-based or vapor-phase deposition is the most mature and widely used method for thin-film growth in the semiconductor industry. Yet, the vapor-phase growth of halide perovskites remains relatively underexplored compared to solution process deposition. The intrinsically largely distinct volatilities of organic and inorganic components in halide perovskites challenge the standard physical vapor deposition techniques. Thermal coevaporation tackles this with independent thermally controlled sources per precursor. Alternatively, pulsed laser deposition uses the energy of a laser to eject material from a target via thermal and nonthermal processes. This provides high versatility in the target composition, enabling the deposition of complex (including hybrid) thin films from a single-source target. This Perspective presents an overview of recent advances in laser-based deposition of halide perovskites, discusses advantages and challenges, and motivates the development of physical vapor deposition methods for hybrid materials, especially for applications requiring dry, conformal, and multilayer deposition.

To ensure the reproducibility of thin film growth, detailed experimental information is essential.In the context of pulsed laser deposition (PLD), critical deposition parameters include: 1) fluence (energy/area J/cm 2 ), 2) deposition or working pressure (and gas(es) employed), 3) spot size on the target (mm 2 ), 4) target composition, 5) target-to-substrate distance, 6) laser frequency, and 7) heater temperature.These parameters are crucial for replicating across different laboratories or PLD vacuum systems.However, as noted in Table S1, many studies fail to provide comprehensive details on these deposition parameters, hindering progress in the field.Beyond properly reporting deposition parameters, other factors such as target preparation, raster and/or scanning patterns on target or of the heater stage, substrate or device stack type, and chamber shape and volume can also impact the reproducibility of results between PLD chambers, even for the same user.Therefore, while reporting deposition parameters should be seen as a guideline, minor modifications are always expected.

PLD of TCOs vs. PLD of MHPs.
The difference between PLD of TCOs and PLD of MHPs comes down to the intrinsic properties of the materials.TCOs (and several metal oxides in general) have higher formation energies than halide perovskites.Therefore, the laser fluence required for target ablation is higher for oxides than for halide perovskites.Specifically, a typical laser fluence used for TCOs is ~2 J/cm², 1 and for halide, perovskites is one order of magnitude lower, i.e., 0.2-0.3J/cm². 2 The UV excimer laser works for both materials because it has an energy greater than the band gap of both (ensuring absorption of the photons).For hardware and process optimization, the requirements are the same for both materials.Both can be deposited at room temperature, but TCOs will be mainly amorphous, while MHPs could already be crystalline as deposited.This difference in crystallinity is again correlated to the low formation energy of the MHPs.
Another difference is the availability of targets.TCO targets are widely commercially available, but halide perovskite targets are not commonly available.As a result, research currently relies on in-housemade targets for MHPs.  3 Precursor ratio must be tuned in the target based on deposition conditions to obtain the desired stoichiometry in the films. 4-situ monitoring of plasma composition and dynamics to understand and predict material transfer. 5

Scalability
Wafer-scale PLD is available.
First industrial PLD demonstrated. 6ser maintenance cost. 7omplex raster scanning patterns of substrate and targets to deliver uniform thin films. 8rge (> 4 inch) halide targets.
Use of alternative laser sources, e.g., high-performance frequencytripled or quadrupled solid-state lasers (Nd: YAG). 7provements in hardware design and automation of processes Material Utilization PLD targets are reusable multiple times. 5e.g., more than 20 depositions in the case of MA1-xFAxPbI3 in 2 .Homogeneous composition through the target thickness after multiple ablations.
In-situ target or film composition analysis to determine when the composition is no longer uniform compared to a fresh target. 5position rates Fast deposition rates can be achieved using highfrequency lasers (> 50 Hz).

Stability
and homogenous ablation of highfrequency lasers.
Current deposition rates of PLD MHPs are at 5 -10 nm/min. 9This is the same challenge as coevaporation. 10velopments on new PLD designs (in terms of target and substrate scanning, as well as laser spot sizes) from hardware to software.

Table S2 .
Summary of advantages, challenges, outlook, and opportunities for future developments of PLD of MHPs.